1. Field of the Invention
This invention relates to a collection assembly, and more particularly, relates to an assembly and method for storing and dispensing additives that are used in preservation, separation or analysis of a blood sample.
2. Description of the Related Art
Blood samples are routinely taken in evacuated tubes. One end of a double-ended needle is inserted into a patient's vein. The other end of the needle then punctures a septum covering the open end of the tube so that the vacuum in the tube draws the blood sample through the needle into the tube. Using this technique, a plurality of samples can be taken using a single needle puncture of the skin.
Collection tubes are conventionally made of glass or plastic. Glass tubes have the advantage of liquid and gas impermeability. Plastic tubes are advantageous over glass in lower breakage, less weight in shipment and easier disposal by insertion, but high permeability to liquid and gas is a disadvantage. For example, polyethylene-terephthalate (PET), though widely used commercially for blood collection, has a limited shelf life due to water permeability.
Blood drawn into a tube is typically mixed with an additive present in the tube prior to draw. Clot activators such as silica particles promote rapid coagulation so that the liquid serum fraction can be readily separated from the clotted cells. Anticoagulants, such as citric acid, heparin or ethylenediamentetraacetic acid (EDTA) are used to prevent clotting when the blood sample is to be used directly in hematological tests or to separate blood cells from the plasma.
The additive, whether procoagulant for clot activation or anticoagulant for clotting inhibition must be rapidly and thoroughly mixed with the blood sample to achieve its end use functionality. If the additive is present in the plastic tube as a solution, water absorption or transmission through the tube must be eliminated to prevent inaccurate additive concentrations. Additives in solution require precise concentrations to obtain reliable tube-to-tube performance.
Therefore, a need exists in the art of blood collection for a means of accurate storage and dispensing of tube additives that reduces dependence on phlebotomist technique and permits use of different plastics for tube manufacture.